1. Field of the Invention
The invention relates generally to the field of wellbore drilling systems and equipment. More specifically, the invention relates to structures for “wired” drill pipe that include a power and/or signal channel associated therewith and that have improved reliability.
2. Background Art
Rotary drilling systems known in the art for drilling wellbores through subsurface Earth formations typically use threadedly coupled segments (“joints”) of pipe suspended at the Earth's surface by a drilling unit called a “rig.” The pipe is used, in association with certain types of tools such as collars and stabilizers to operate a drill bit disposed at the longitudinal end of a “string” of such pipe joints coupled end to end. As a wellbore is drilled, and it becomes necessary to lengthen the string of pipe, additional joints of pipe are coupled to the string by threading them onto the upper (surface) end of the string of pipe. Removing the string of pipe from the wellbore, such as to replace a drill bit, requires uncoupling joints or “stands” (segments consisting of two, three or four coupled joints) of the pipe string and lifting the string from the wellbore. Such coupling and uncoupling operations are an ordinary and necessary part of drilling a wellbore using a rig and such pipe strings (“drill strings”).
It is known in the art to include various types of measuring devices near the lower end of a drill string in order to measure certain physical parameters of the wellbore and the surrounding Earth formations during the drilling of the wellbore. Such instruments are configured to record signals corresponding to the measured parameters in data storage devices associated with the measuring devices. The measuring and storing devices require electrical power for their operation. Typically such power is provided by batteries and/or a turbine powered electrical generator associated with the measuring devices. The turbine may be rotated by the flow of drilling fluid (“mud”) that is pumped through a central passageway or conduit generally in the center of the pipes and tools making up the drill string. It is also known in the art to communicate certain signals representative of the measurements made by the devices in the wellbore to the Earth's surface at or close to the time of measurement by one or more forms of telemetry. One such form is extremely low frequency (“ELF”) electromagnetic telemetry. Another is modulation of the flow of mud through the drill sting to cause detectable pressure and/or flow rate variations at the Earth's surface, called “mud-pulse telemetry.”
The foregoing power and telemetry means have well known limitations. It has been a longstanding need in the art of wellbore drilling to provide electrical power and a relatively high bandwidth communication channel along a drill sting from the bit to the Earth's surface. Various structures have been devised to provide insulated electrical conductors in association with drill pipe to provide such power and signal channels for a drill string. The features of the structures that have been developed for such insulated electrical conductor channels are related to the particular requirements for pipes used for drill strings, namely, that they must be made so as to cause as little change as possible in the ordinary handling and operation of drill pipe. As will be appreciated by those skilled in the art, such handling includes repeated threaded coupling and uncoupling. Use of the pipe string during drilling will result in application to the pipe string of torsional stress, bending stress, compressional and tensional stress, as well as extreme shock and vibration.
One type of “wired” drill pipe is described in U.S. Patent Application Publication No. 2006/0225926 filed by Madhavan et al. and assigned to the assignee of the present invention. The wired drill pipe disclosed in the '926 publication includes a conduit for retaining wires in the wall of or affixed to the wall of a joint of drill pipe, as well as electromagnetic couplings for the wires proximate the longitudinal ends of the pipe joint. The electromagnetic coupling is typically disposed in a groove, slot or channel formed in a portion of the treaded coupling called a “shoulder” or thread shoulder. A thread shoulder is a surface that extends substantially laterally (transverse to the longitudinal axis of the pipe) and is included to perform functions such as transferring axial stress across the threaded coupling to the adjacent pipe joint, and to form a metal to metal seal so that fluid pressure inside the pipe will be retained therein. It has been observed that the groove or slot in wired drill pipe may be failure prone.
There continues to be a need for improvements to structures for wired drill pipe to increase their reliability and ease of handling during drilling operations.